Medium and heavy duty packaging boxes are typically manufactured from corrugated cardboard. Corrugated cardboard sheet stock is cut into appropriate dimensions, slots and folds are created in the cardboard at appropriate positions, and two ends of the cardboard are glued together to form a continuous loop. These operations are typically performed in a commercially available machine capable of performing all of the folding, slotting, and gluing operations. The resulting product is then shipped to the customer who then folds the cardboard at the appropriate positions to form a normally rectangular tube, and uses the flaps created by the slots to form the two ends of the box.
With corrugated cardboard which is manufactured from 100% virgin paper fibers, the slots are typically formed using slotting blades having sharpened edges separated by a gap corresponding to the width of the desired slot. One or more slotting blades are mounted in a rotating slotter head above the level of the cardboard sheet stock and between two female blades located below the cardboard sheet stock. The outer sides of the male blade interact with the interior sides of the female blades to shear the slot from the cardboard in a scissor-like fashion. Since the natural fibers are relatively weak, the slots formed are relatively clean with few fibers pulled from the cardboard, and little fraying of the edges.
However, with today's marketplace, it is uncommon to manufacture corrugated cardboard from 100% virgin paper fibers. Corrugated cardboard is now commonly manufactured from a combination of virgin paper fibers, recycled paper fibers, and synthetic fibers. Conventional slotting blades used to create slots in 100% natural fiber cardboard cannot create a cleanly shaped slot in that the recycled paper fibers are often not cleanly severed by the slotting blade. Rather, the recycled paper fibers are grasped by the male slotting blade and pulled from the cardboard sheet stock resulting in frayed edges and a non-uniformly shaped slot.
Since the ultimate end users of the cardboard boxes are often from the food industry, or other industries where cleanliness, and the appearance of cleanliness, are of utmost importance, such frayed edges are not acceptable. They create not only the impression that the box is sloppy, but also that the product inside is also sloppy and less than aesthetically desirable.
More recent prior art blades have incorporated the use of teeth or serrations along the cutting edges which are better equipped to cut through cardboard than are conventional blades having curvilinear cutting surfaces. The machining procedures used to form the blades typically result in serrations on both sides of the cutting blade which are aligned in matching sequence such that corresponding serrations penetrate the cardboard along the same axis line across the slot. Therefore, the profile of each side mirrors the other side and results in fewer locations around the blade at which the serrations perforate and penetrate the cardboard. This results in less complete shearing of the slot, more pulling of fibers from the sides of the cardboard adjacent the slot, and thus more frayed edges.
In addition, with the increased use of recycled fibers in the production of corrugated cardboard, the blades used to create the slots in the cardboard are confronted with increasingly abrasive fibers which eventually fragment the cutting edges and dull the blade. Conventional blades are provided with sharpened edges only at the joints between the cutting surface and the opposing sides, and once these are fragmented or worn down, their cutting efficacy is lost. While the more recent blades alluded to above do include serrations along the cutting edges, the serrations are also only along the edges, and once they are fragmented or worn down, their cutting efficacy is lost as well.